The Obama administration, after months of prevarications on Syria, has signaled a willingness to do more than bluster during press conferences and send humanitarian supplies. Supportive rhetoric and blankets are clearly not enough, and military options are under review. But U.S. options in Syria have narrowed from early-stage levers of influence to last-ditch efforts to stanch the bleeding.

The president has decided to do something, but what?

It is late in the conflict for a major shift in U.S. policy. This has put American interests at a disadvantage not merely against Assad, but also against the other invested external parties. Everybody who might pick and back a proxy in Syria has already done so, except the U.S. and its NATO allies.

President Obama might enhance both overt and clandestine U.S. efforts, or he could pull back even further in the face of rapid deterioration. Whether he picks the Serbia model of direct U.S. intervention, or the Sudan model of looking the other way while the country burns, or something in between, his preferred option must be determined sooner rather than later. The closer Syria gets to the endgame for Assad, the harder it will be for America to have any say in the outcome.

Despite the late hour, three general strategies are still open to America in Syria:

1. Cordon and contain. This entails blocking off cross-border spillover of the damage and more or less letting Syrians fight it out among themselves. But even this policy would maintain a baseline level of support for regional allies and of the humanitarian assistance already in place. The U.S. has taken some measures to secure international borders, such as installing Patriot-missile batteries in Turkey, and the creation of a protected refugee safe zone could soon follow.

After two costly wars to assist largely ungrateful populations in the Middle East, the American urge for a minimalist approach is understandable. But Syria’s spiraling humanitarian disaster will put pressure on the administration — which once invoked the “responsibility to protect” doctrine as the reason for its Libyan intervention — to do much more in the Levant.

Some might argue that “cordon and contain” is indifferent to human suffering. Others will point out that the whole policy could collapse if the conflict spreads into Lebanon, Iraq, or southern Turkey. The desire to avoid a quagmire, however, remains strong, and the memories of recent American interventions in the Middle East are fresh.

President Obama may retreat into “cordon and contain” as the least bad option.

2. Assist and advise. Insurgencies often lack logistical skills, intelligence support, and competent training. Outside allies can be critical in making up for this shortfall. Right now the U.S. is engaged in a low-impact, low-risk version of this approach.

There are plenty of press reports about direct assistance to factions of the rebels by U.S. intelligence officers, and the training of anti-Assad brigades in Jordan indicates a renewed seriousness in the White House. This advisory and training component will grow in importance, as finding critical Assad-regime targets — including chemical weapons — will require actionable intelligence and the communications infrastructure to move on it.

The “assist and advise” strategy has an inherently limited impact on the ground, and it suffers from the difficulties of operating in a confused, rapidly changing conflict environment. A faction that is friendly to the group known as al-Qaeda in Iraq and Sham (AQIS) — Sham is the classical-Arabic name for greater Syria — may be the most effective proxy in some parts of Syria, forcing U.S. intelligence officers to make tough calls on the spot.

The Obama administration is likely to ramp up its “assist and advise” efforts in the months ahead. Of course, events on the ground could quickly transform this posture into full-fledged intervention, particularly if U.S. assets or allies were directly threatened.

3. Close air support and commandos. This is the deepest level of U.S. intervention currently under consideration. It would involve some combination of a no-fly zone, aerial strikes on Assad-regime targets, and the insertion of Special Operations troops into the theater.

The ability to degrade Assad’s military capabilities and to work hand in hand with specific rebel factions would have the benefits of helping overthrow a sworn enemy in Damascus and establishing alliances on the ground. But U.S. personnel and assets will be at greatest risk if the administration picks this path. Obama has thus far stopped short of any overt military action against Assad primarily for that reason.

Full-fledged U.S. invasion seems to be off the table — unless Assad widely deploys chemical weapons. There is simply no appetite among the majority of Americans for another police action and nation-building effort in an Arab land.

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Whichever option Obama chooses, implementation speed is an increasingly critical factor. The Obama administration must adopt a new strategy with a sense of urgency. Last month was Syria’s most violent yet, and the jihadist elements of AQIS are ascendant. Its merger with the Syrian rebel group Jabhat al-Nusra could prove disastrous in a post-Assad Syria. And with every passing day, other outside actors like Iran and Hezbollah strengthen their proxies.

President Obama has been slow to act on Syria. While our commander-in-chief still has time to influence a better outcome in a desperate situation, the window is rapidly closing. If America is to lead, even from behind, the time to do so is now.

— Buck Sexton is a former CIA officer in the CounterterrorismCenter and the Office of Iraq Analysis. Currently, he is co-host of Real News on The Blaze TV.